During the drilling of a well containing oil or another effluent (in particular gas, steam, water), it is known to analyze the gaseous compounds contained in the drilling muds emerging from the well. This analysis facilitates the reconstruction of the geological sequence of the formations passed through during the drilling process and helps to determine possible uses for the fluid deposits encountered.
This analysis, which is carried out continuously, includes two main phases. The first phase consists in extracting the gases conveyed by the mud (for example, hydrocarbon compounds, carbon dioxide and hydrogen sulphide). The second phase consists in qualifying and quantifying the extracted gases.
A degasser having a mechanical stirring means of the type described in FR 2 799 790 is frequently used for extracting the gases from the mud. The gases extracted from the mud, which are mixed with a carrier gas introduced into the degasser, are conveyed by suction through a gas extraction conduit up to an analyzer, which allows the extracted gases to be quantified.
A method of this type is not entirely satisfactory, especially for oil or synthetic product-based muds. The kinetics for the extraction of the gases from the degasser is, in particular, dependent on the solubility of the gases in the mud. For example, for an oil drilling mud, C4 hydrocarbon gases are extracted more slowly than C1 hydrocarbon gases.
Given the limited residence time of the mud in the degasser, determining the relative or absolute content of the gases contained in the drilling mud from quantities of gases extracted from the degasser requires complex mathematical models and is imprecise.
The main object of the invention is therefore to determine, in a precise yet simple manner, the content of at least one given gas contained in a drilling mud, during a drilling process.